Comparison of three occlusal splint material systems manufactured by conventional, subtractive, and additive techniques

OBJECTIVES: To compare the thermal-viscoelastic behavior, hygroscopic properties, color stability, and surface morphology of three commercial occlusal splint material systems produced by conventional heat polymerization, CAD/CAM milling, and 3D printing. The null hypothesis was that the three material systems would not differ in thermal-viscoelastic behavior, hygroscopic properties, or color stability. Surface morphology was assessed qualitatively as a complementary outcome. MATERIALS AND METHODS: Heat-polymerized polymethyl methacrylate (HEC), CAD/CAM-milled polymethyl methacrylate (CAD-M), and a 3D-printed photopolymer resin (3DP) were evaluated. Dynamic mechanical analysis was performed to determine glass transition temperature (Tg), tan δ, and thermal heterogeneity (n = 5). Water sorption (WS), solubility (SL), and color change after coffee immersion (ΔE00) were assessed (n = 8). Surface morphology was qualitatively analyzed by atomic force microscopy and scanning electron microscopy. RESULTS: Significant differences were observed among the material systems for thermal and hygroscopic outcomes. CAD-M presented the highest mean Tg (149.58 ± 0.95 °C), the lowest water sorption (18.76 ± 0.56 µg/mm³), the lowest solubility (2.59 ± 0.48 µg/mm³), and a ΔE00 of 2.29 ± 1.20 after 7 days of coffee immersion. Conversely, 3DP showed the lowest Tg (83.18 ± 7.87 °C), highest WS (35.12 ± 0.82 µg/mm³), highest SL (6.16 ± 0.40 µg/mm³), greatest color change, and a more irregular surface morphology. CONCLUSIONS: The three evaluated commercial material systems differed in thermal-viscoelastic behavior, hygroscopic properties, color stability, and surface morphology. Among the specific systems tested, CAD-M showed the most favorable overall laboratory profile. Because each manufacturing approach was represented by a single commercial material with a distinct composition, these differences cannot be attributed exclusively to the manufacturing route. CLINICAL RELEVANCE: Under the in vitro conditions tested, the milled material system showed a higher glass transition temperature and lower water sorption, solubility and coffee-induced discoloration than the 3D-printed system. Whether these laboratory differences translate into differences in the clinical performance of occlusal splints was not assessed in this study.